1. Native DNA from Bacillus subtilis was fractionated by stepwise elution from methylated albumin, the transforming activity being confined to two out of four fractions. Partial separation of DNA active in transformation for the arginine marker from that showing activity for the histidine and tryptophan markers was achieved. 2. Partial denaturation of DNA at 90° and 93·5° resulted in the preferential destruction of transforming activity for the histidine and tryptophan markers. 3. Denaturation of DNA at 100° followed by chromatography on methylated albumin yielded five fractions, two of which exhibited residual activity. Redenaturation at 100° resulted in the interconversion of four out of the five fractions. Redenaturation of fractions labelled with 15N and 2H suggested the presence of a specific component that did not readily take part in the interconversions.
